Dyes are widely applied in biological research and medical diagnosis. The dyes may, in vivo or in vitro, mark biological material (such as amino acids, peptides, proteins, antibodies, biological polymers, cells, or tissues). If the dyes can be synthesized in great quantities to collocate with automatic inspection, the dyes can be used to mark biological material.
The Rhodamine dye family is one of current major dyes. However, the rhodamine structure is inherently water insoluble. As such, a hydrophilic group (e.g. sulfonic acid) should be grafted to the rhodamine structure to allow the rhodamine dye to dissolve in water for marking the biological material. A combination of factors, including the ratios of the concentrations between the dye and the biological material, the photoluminescence efficiency of the combination of the dye and the biological material, and method of grafting the sulfonic acid to the rhodamine structure should be simultaneously considered.